Participant Accrual and Retention Unit (PAR). The HNRC cohort, recruited and retained by the PAR Unit, consists of approximately 300 HIV+ individuals and HIV- controls who have undergone prospective, multidisciplinary evaluation. Data from this cohort are the foundation for the Center's scientific productivity, including presentafions, publications, and preliminary investigations that have led to development of R01s and other peer review grants associated with the HNRC. The PAR Unit maintained a directory of research participants that served the dual purpose of identifying participants who might be suitable for specific research programs, while also preventing "overuse" of such participants. Training by the PAR Unit in participant identification, recruitment, obtaining informed consent, including determining capacity to provide consent for cognitively impaired persons, helped launch and sustain successful recruitment efforts in many other studies.